The C—C bond in C₂H₄ is stronger than in C₂H₆ because it has more hydrogens.

The C—C bond in C₂H₄ is stronger than in C₂H₆ because it has a higher bond order.

The C—C bond in C₂H₆ is stronger than in C₂H₄ because it has a higher bond order.

The C—C bond in C₂H₄ and have equal strengths because they have the same number of carbons.